Method and apparatus for removal of silica vapor from steam



Jan. 12, 1965 P. B. PLACE 3,165,387

METHOD AND APPARATUS FOR REMOVAL OF SILICA VAPOR FROM STEAM Filed Dec. 27. 1961 INVENTOR: PALMER B. PLACE ATTORNEY FIG. 2 I BY United States Patent The presentinvention relates to a'novel means and method for purifying steam and more' particularly" to; a

washingapparatus for removing vapo'rous' impurities such w as silica vapor from high 'pre'ssure'steam produced in a steam generaton It has long been known that the steam produced in high pressure steam generators-contains both solid'- and vaporous impurities.

, 'means' employed in such generators are *c'apabl ofj'le moving. the solid impurities associated'withthe moisture entrained in the steam: such means cannot: remove those impurities which exist' in vaporous form. As aresult, th'ese impurities'are carried to the turbine or other'work producing meanswh'ere'their deleterious effects ar'e'real- 1 ized. a v

@Silica is one of the forms of 'impurities prevalent in' high pressure steam. It" is found dissolved in-theboiler *water'and forms silicic-acids which have 'sufiicient vapor, pressure in alkaline solution t-oresult in the vaporization of a smallffraction' of the silica: When mixed with the generated'steam; the vaporized silica cannot be's'eparated by mechanical separator devices'and thusiscarriedover to the turbine or; other' work performing means where '1 the pressure and temperature of theEsteam vas well as that of the vaporized impurities are reduced c'ausing'the solubilityof the silicain the steam to be lowered thereby resulting in the formation-of solid depositsf 'silicat:0n=

the internals of-the turbine: or other such'idevice's; Such deposits ultimately result-finthey complete shutdown of the work producingiunit sothat=th,e internals-thereof can be cleaned or replaced; I h

t It has been-found that removalgof vaporo'us isilica' from steam can" be-achieved-"bycontacting steaml createdtin the' generator, with relatively pure-waterfwhich absorbs While the mechanical separating 3,165,387 Patented Jan; 1 2:, 1965 ICE it serves'to wash'the steam and then to-the steanrgenerator tubes" where it istransformed into steam. While -st'lcha-concept is employed'in'wa'shers of existing design its use is limitedby the fact that it excessive amounts ofi wash waterareemployed in the washer there is a 1 danger thatthewater' will be carried by the st'eam into the "screen drier located at the steam outlet causing flood- 'ing of :the drier' thereby rendering it ineffective to dry the steam passing therethroug'h. Due tothe lack of avail'able"sp'ace'withinthe-steam and water drum which house's tlie washing apparatus and the drier it' virtually impossible to provide suflicientfspac'e between-thelwasher andthe' drier inorder to preventcarryover ofwater to the drier when large amounts of waterare emp'loy'ed in the washer. Thereforegin order'to'employ conventional steam washing 'units'withima stea'in and water'dfrum which houses the s'tearri drier it is necessary tolimit th e (amount of water admitted tothe washer. This 'renders it difiicult to admit all of the feed-water totli'ewa'slier," especially at high steam" generator loads where a lar'ge ai'rro'unt of feedvvat'erlis' being fed'to the drum} .By meansof the rese ntinvention a riovel'stea-m washer apparatusand method"'are provided which permits utilizationofallof thefeedwater? being-fed m the steamgeri- .It is alsoanobject'of p ascoinp'actsteam washing means and 'rnetho'd'iincorporatting eachfof the aforementioned essentials'for eflicient the silica frorn'the steam and returns itito the boiler water I V test the tially free ofvharmiul contaminants: I a

I a In order to-achieve aghightefiiciency of silica removal the following factors must: be considered. Firstly the water.

Silica re rersmiaiconcentration' of silica in" the "wash water as t .faga'instthat carried in the ,steam. flfherefore the amount in the system where it can" be" ultimately removed by .blowdown. The steam wh'ich emerges from :the generator unit after washing -i stherefore"renderedjsubstandrum; incorporating asteam Washer of-the presentinvenotion; and:

wash water employed mustbelof; a relatively high purity steam. Secondly, there mustl be {provided rneans to efintimatecontact of all io fathe steam with the wash oval from "steam is dependent uponthe difa so as a to permit maximum tabso rptionfof silica Iinthe *drumof existing steam generators." 40 'compactsteamwash'ing.apparatus and method'which are: ,capablelof utilizing a'll of,the feedwater being: fed-to the erator with no dan'ger ofi carryovert'o and flooding. of,

It'is therefore a principle object-of thepresent'inven- V tion to provide novel apparatusfand method. which will fefiiciently' remove substantially all ofthe entrained vaporous silica from the highupressuresteamproduced i'n'"a steam generator}; t v the present invention to provide steam purification. t I

'- Aistill further object oftheinvention is to' provide a t compact steam'washingQappara-tus and-method which'can and vapor be arranged within the confines er the liquid tAn additiorialtobject; of thegihvention is 'to provide a steam generator unit:

' Additional objects andadvantages willbecome ap s ent-iifrom the illustrative descriptioniwhenvread in con juunction with the iollowing ,drawin'g intwhich: 1

" FIGURE 1 is a transversesection of: a vapor and liqui FlGUREl-is' a tastedan view of the Start and 1 I I water drum 10 of a steam generator unit comprising an oig'fsilic-a which can be removed from thesteampassing through the washer variesxwith eithertheamount 'ofwash -waterfpassing through the unit orzthepurity of the wash ,w'a'ten'for both. t. Where the amount of water which can a fbefhandledlby a washer unitxis liinited, ,.more care must be'ft ake'n to insure that the. purity of thewash water be such asjwillt reduce the? silica concentration in the steam V to acceptable limits. tByQ-the same: token, where a great amount oi wash water'can hefeinp loyed in a washer the upper steam space 1'1 anda lower water space 12? defined by the'norma-lwlevelof -boil er' water in the drum. Conduit 1;? is positioned at;the,top; of; the drum'commuriicatingwith steam space'll proyiding a; means for de livering the steam; created; in thef'steam; generator to '3 steam-util izing' device. -v A screen drier 14' is positioned ,in-thesteam path" closely "adjacent the steam outlet.13 and-secured in place by means of a pluralityof brackets which 'areattachedto'the inner surface'ofithefdrum.

A'lo'rig thev 'lowe r l eft-hand portion of the-drumll); as

viewed in FIGUREJ, is provided a p a y of struc-' I vtural members" 17 through 1 9 which formachamher 16 extending along substantially the entire lengthcf Ethe drum, Circular ,endplates (-CEIGUREZ) are attached T :at either l-emillo fchamber hg 'andto the inner surface of thefdrum thereby isolatingthe chanibe vfrom the reh'jmainder ofi'theidrum"interior. Y p v Steam 'generatortubes 21 'communicate'with' the chain a team andwater mixturewhich has j I --throughsteam outletlli asa substantially puregfdryivapor. direct'mg' the steamintothe low/elocitysteam p ced been created furnace portion of the steam gener-v ator into the chamber. Downcomer tubes 22 communicate with the water space 12 of drum and provide I means for recycling water which falls to theglower portion of the drum through the steam generator.

The separators shown in FIGURE 1 comprise an elon- .gated cylindrical can 24 having a swirl inducing bafiie means positioned at the inlet thereof which; imparts therethrough thereby removing by centrifugal. action the heavy elements contained in the 'mixture. K These elements, consisting of water and solid entrainments found in the mixture are discharged from the outlet of the separator. and fall into the drum water space 12. The disclosed centrifugal se parators are of a type similar to that described in U.S. Patent 2,646,397; to Raveseiet al.,- of August :11, 1953, Y

a rotary movement to a steamand watermixture passing Communicating with chamber 16 through the chamwhich permit passage of a portion of thesteam and water ixtureito a'row of similar separators which line the right:

hand side of the drum 10. II I Each-row of separators-is enveloped by aplurality of partitions 27, through? whichpartiallysurroundflthe separators forming discharge passages through which the discharge from the separators is directed toward the .Water space. '12, I Secondary separator, means comprising a plurality of closely spaced, corrugated plates 31; is posi; I tioned between partitions 28' and29 and is attached thereto. The secondaryseparator'provides a means for fur-' ther segregation, of the vapor which-emerges from the; centrifugal vseparators; Discharge from the 'plates- ;31{-ffalls to the waterspace 12. 7

corrugated her side wall partition 17- is: a row, off-crossover tubes 26,;

4 and compelling it to abruptly change its direction in order to flow upwardly out of the steam outlet 13 a portion of the water entrained in the steam is caused to be gravita-' tionallyremoved therefrom thereby decreasing the load on the screen drier 14 and permitting the drier 14 to receive steam of such awater content thatthe drier iscapable of handling withoutbecoming'fiooded;-. V e I I The" operation of the device is as follows. The steam andwater mixture generated' in the steam. generator unit is deposited into the. chamber 16 by means of the riser tubes 21 from whence it passes throughthe dual rows of separator apparatus; emerging therefrom as substantially dry steam. The steam risestowar'd the'top of the drum around the inner surface thereof and is directed toward the-upper surface of matting 35. Atithis point relatively pure feedwater which isrlsupplied to the'unit by means of elongatedtube 33 I gravitationally emerges therefrom through apertures;34 and, falls downwardly into the steam fiowpath andjthroughthe washer matt material The water which emerges from the washer is; directed toward thejwater space 12 by means of the bafliexplates 27 and 28 and the steam which emerges from :the washer is v directed upwardly due to-its lesser density through the Overlying the row of separator units is a steam washer unit 32. .The steam, washer unit, 32'con1prises a wash water inlet means 33 and an elongated mass of closely compacted wire mesh matting 35; The materialrforrning V the wire mesh matting 35 is supported by structural'mem- 1 bars 36 and 37 which constitute a frame therefor withthe. respective members being attached 'to ,member 28 and screen drier support 15;":1 2

The wash water-inletgm'eans comprisesi an elongated screen drier 14 which removes any'liquid which may be retained inf-the steam therefrom. The steam which emerges, from ,the steam outlet is therefore substantially pure, dry steam.

The steamwas'her unitoftheinstantinvention achieves I a steam washing; efiiciency of'high order. Steam emerg-v ing' from the steam outlet exhibits agred'u'ction ofvapor ,contentafrom between'i801and 90 percent. Efiiciency' of ,this order. is attributed tozthe purity iof-the wash water and the amount of wash water'utilized; Thefdownward flow; of steam and-Washwater'ina direction awayfrom the steam drier 14 obviates anydanger of floodingthe-screen drier when excessive amounts of wash'waterare directed into the matting; Such a feature makes it possible to use all of thefeedwater. being fed-to the steam generator as ;a steam washing medium thereby. obviating the necessity havingnto provide'means-to' direct'only a portion of the feedwater to the wash water unit.

tube 33 having a plurality of longitudinally spaced aper a lesssteel wire which forms 'ailoosely woven mesh. The

mesh is compacted to adensity "of approximately 12 pounds per cubicfoot while maintaining 'a free area of approximately 90 percent." 'Such a matt structure gives ,tures 3A which permit incoming wash waterto be directed I downwardly intothe matt 35.';-;Thewire meshmatt is 1 I preferably formed of a plurality of layers of Goodlo'eiwire' 'mesh packing,.thef thickness'being approximately from 2' to '3 inches; The mattis constructed of lightgaug'e stainthe steamfample room to freely pass throughgthe Washer I .yet alsoprovides a means whereby the steam will becornpelled'to comein contact with the wash water which flows though the matt. 1 Q I The washer unit 32 is locatedin the steam "path between cause it is heavier than' the steam emerging therefrom; is

dir ected downwardly byfimeans .of structural members '27 I and 28 into the water space 12 where itcanberecycled through fthe; generator: ".Thejsteamfwvvhich flows into steam space" 11', L because it is less" dense? tlranthe water,

flows upwardly through'the'screen drier '14 andernerges I washer comprising an inletincommunication'with said separator means vaporloutletia" vapor washer outlet positioned below/"said vaporv washr inlet, means for effecting the intimate contact ofvapor and wash water positioned" between said 'wa'sher f inlet and outlet, means positioned 3 sabovesaid inlet for-gravitationally supplying washlwater I to said contact-efiectinjg meansin a directionf cocurrent' .Wh-ile. there has been disclosed a particularl ernbodiment of the invention this disclosureisintnded to'merely' illustrate and not to limit the, inventive jconcept. It is understood that changesmay'lbe made in theform'of the V apparatus disclosed with eappended claimsL' What is claim'edisi: Y 1. In combination with 'a'vap or and liquid drum having an inletgfor introducinga'vapor and liquid mixture thereto and a vapor outlet opening positioned-in the upper portion of said drum including ascreendrierzpositioned close- I 1y adjacent to and'extendin'g across said vapor outlet opening, vaporpurifying apparatus comprising separator means including: a :rnixtu're iinlet communicating with the drum inlet and ai vapor outlet adapted to remove liquid particles from said mixture, j a vapor washrinter'posed between said separator-means and said screen drier,'means forming an expansion space providing a low velocity vapor space Y between: said washerandisaidscreen drier, said vapor 'out departing from-the spirit of -theinven'tion coveredb th with 'downwardly flowing 'vapor'throug'h, saidwa h dj I tionfaway, fro

in contacttherewithf said screen dr'ier being positioned.

above said washer outlet'whereby said washer outletcorrrmunicat'eswithls id lowf'velocityj vapor spaceih afdirec aid screen drier thereby Cal'l sing' the' vapo'r ischar'ge from' s'aid washer outle hang; of direction inrsaid lowve under forming an expansion space providing .a low velocity vapor space between said washer and said screen drier, said vapor washer comprising an inlet in communication with said separator means vapor outlet, a vapor washer outlet positioned directly below said vapor washer inlet, a mass of woven wire mesh for effecting the intimate contact of vapor and wash water positioned between said washer inlet and outlet, means positioned above saidwasher inletrfor gravitationally supplying wash water to said woven wire mesh in a direction cocurrent with downwardly flowing vapor through said washer and in contacttherewith, said screen drier being positioned above said washer outlet whereby said washer outlet communicates with said low velocity vapor space in a direction away from said screen drier thereby causing the vapor discharged from said washer outlet to undergo an abrupt change of direction in said low velocity vapor space ahead of said screen drier.

3. In combination with a vapor an inlet for introducing a vapor and liquid mixture thereto and a vapor outlet opening positioned in the upper porand liquid drum having 7 inlet, a mass of woven wire mesh for effecting the intimate contact of vapor and wash water positioned between said washer inlet and outlet, means positioned above said washer inlet for gravitationally supplying wash water so said woven wire mesh in a direction cocurrent with downwardly flowing vapor through said Washer and in contact therewith, said screen drier being positioned above said washer outlet whereby said washer outlet opens into said low velocity vapor space below and in a direction away from said screen drier thereby causing the vapor dischargedfrom said washer outlet to undergo an abrupt change of direction in said low velocity vapor space ahead of said screen drier.

4. A method of removing vaporous impurities including slica vapor from vapor and liquid mixture supplied to the vapor and liquid drum of a vapor generator having an elevated vapor outlet and a screen drier located immediately therebelow comprising the'steps of mechanically separating liquid particles from said mixture, passing the separated vapor downwardly through a mass of woven wire mesh the lowest portion of which is positioned below said screen drier while simultaneously directing wash water downwardly into said mass of woven wire tion of said drum including a screen drier positioned closely adjacentl to and extending across said vapor outliquid particles fromsaid mixture, avapor washer interposed between said separator means and said screen drier, means forming an expansion space providing alow velocity vapor space between said washer and said screen drier, said-vapor washer comprising an inlet in communication with said separator means vapor outlet, a vapor washer outlet positioned directly below said vapor washer mesh cocurrent with the flow of said vapor and in contact therewith to remove vaporous impurities including tationally separating particles of wash'water entrained in said vapor by the abrupt upward change of direction the vapor makes before it enters said screen drier, discharging the spent wash water in a direction away from said screen drier and thereafter drying said vapor in said i screen drier. J,

References (Iited in the file of this. patent UNITED STATES PATENTS 2,648,397 Ravese et a1 Aug. 11,1953 2,875,992 Pirsh et a1 Mar. 3, 1959 2,895,566 Coulter July 21, 1959 3,006,436 Starbuck Oct. 31, 1961 Sexton Feb. 27, 1962 

1. IN COMBINATIN WITH A VAPOR AND LIQUID DRUM HAVING AN INLET FOR INTRODUCING A VAPOR AND LIQUID MIXTURE THERETO AND A VAPOR OUTLET OPENING POSITIONED IN THE UPPER PORTION OF SAID DRUM INCLUDING A SCREEN DRIER POSITIONED CLOSELY ADJACENT TO AND EXTENDING ACROSS SAID VAPOR OUTLET OPENING, VAPOR PURIFYING APPARATUS COMPRISING SEPARATOR MEANS INCLUDING A MIXTURE INLET COMMUNICATING WITH THE DRUM INLET AND A VAPOR OUTLET ADAPTED TO REMOVE LIQUID PARTICLES FROM SAID MIXTURE, A VAPOR WASHER INTERPOSED BETWEEN SAID SEPARATOR MEANS AND SAID SCREEN DRIER, MEANS FORMING AN EXPANSION SPACE PROVIDING A LOW VELOCITY VAPOR SPACE BETWEEN SAID WASHER AND SAID SCREEN DRIER, SAID VAPOR WASHER COMPRISING AN INLET IN COMMUNICATION WITH SAID SEPARATOR MEANS VAPOR OUTLE,T A VAPOR WASHER OUTLET POSITIONED BELOW SAID VAPOR WASHER INLET, MEANS FOR EFFECTING THE INTIMATE CONTACT OF VAPOR AND WASH WATER POSITIONED BETWEEN SAID WASHER INLET AND OUTLET, MEANS POSITIONED ABOVE SAID INLET FOR GRAVITATIONALLY SUPPLYING WASH WATER TO SAID CONTACT-EFFECTING MEANS IN A DIRECTION COCURRENT WITH DOWNWARDLY FLOWING VAPOR THROUGH SAID WASHER AND IN CONTACT THEREWITH, SAID SCREEN DRIER BEING POSITIONED ABOVE SAID WASHER OUTLET WHEREBY SAID WASHER OUTLET COMMUNICATES WITH SAID LOW VELOCITY VAPOR SPACE IN A DIRECTION AWAY FROM SAID SCREEN DRIER THEREBY CAUSING THE VAPOR DISCHARGE FROM SAID WASHER OUTLET TO UNDERGO AN ABRUPT CHANGE OF DIRECTION IN SAID LOW VELOCITY VAPOR SPACE AHEAD OF SAID SCREEN DRIER. 